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Axelar CGP Sui

An implementation of the Axelar cross-chain contracts in Move for the Sui blockchain.

Installation

Install Sui as shown here

Install node.js 18+

Build all Move packages

npm ci

npm run build

Testing

Run tests for all Move packages

npm run test

Coverage

To run code coverage, Sui debug binary needs to be built locally. You can also see coverage reports from the GH actions.

brew install libpq
brew link --force libpq
npm run coverage

See .coverage.info for the coverage report.

Development

Install the Move extension in VS Code. It should come pre-installed with move-analyzer.

Move Book: https://move-book.com Move Examples: https://examples.sui.io

Sui framework dependency is pinned to a specific mainnet release for all packages for consistency.

Deployment and Operations

Official Sui deployment and operations scripts can be found here.

Release Process

Please check the release process for more details.

Gateway

The gateway lives in a few modules but has all of its storage in a single shared object called AxelarSigners.

Relayer Spec

Relaying to Sui is a bit complicated: the concept of 'smart contracts' is quite warped compared to EVM chains.

The Problems

Firstly, all persistent storage stems from Objects that have the key property and are either shared or owned by an account. These objects have a specific type, which is defined in a certain module, and only that module can access their storage (either to read or to write to it). This means that instead of calling a smart contract with some data, in Sui one needs to call a module, pass the Objects that are to be modified as arguments, alongside extra arguments that specify the kind of change that should occur. This additionally means that the concept of msg.sender does not apply to applications, and a certain capability object that functions like a 'key' to unlock certain functionality needs to be used instead.

The second issue is the lack of interfaces whatsoever. It is impossible for a module to ever call a module that is published at a later time. This means applications that want to interface with future applications must be called by those future applications, but need to call pre-existing ones. To expand on this, we expect contract calls that are received to potentially modify the storage of multiple objects in a single call, which makes it impossible to require modules to implement a 'standardized' function that a relayer will call, because the number of arguments required varies depending on the application (or the type of call).

Finally, we do not want to require the payload of incoming calls to have a certain format, because that would mean that working applications that want to exapnd to Sui need to redesign their working protocoll to accomodate Sui, discouraging them from doing so.

The Solutions

First of all, as we mentioned before, for applications to 'validate' themselves with other applications need to use a capability object. This object will be called Channel, and it will hold information about the executed contract calls as well. It has a field called id which specifies the 'address' of the application for the purposed of incoming and outgoing extenral calls. This id has to match the id of a shared object that is passed in the channel creation method (alongside a witness for security). This shared object can easily be querried by the relayer to get call fullfilment information. Specifically:

  • The shared object has to have a field called get_call_info_object_ids that is a vector<address>.
  • The module that defined the shared object type has to implement a function called get_call_info, which has no types, and takes the incoming call payload as the first argument, followed by a number of shared objects whose ids are specified by the get_call_info_object_ids mentioned above. This function has to return a std::ascii::String which is the JSON encoded call data to fullfill the contract call.
  • This calldata has the following 3 fields:
    • target: the target method, in the form of package_id::module_name::function_name.
    • arguments: an array of arguments that can be:
      • contractCall: the ApprovedMessage object (see below).
      • pure:${info}: a pure argument specified by $info.
      • obj:${objectId}: a shared object with the specified id.
    • typeArguments: a list of types to be passed to the function called

ITS spec

The ITS on sui is supposed to be able to receive 3 messages:

  • Register Coin: The payload will be abi encoded data that looks like this: 4: uint256, fixed, tokenId: bytes32, fixed, name: string, variable, symbol: string, variable, decimals: uint8, fixed, distributor: bytes, variable, mintTo: bytes, variable, mintAmount: uint256, variable, operator: bytes, variable, Don't worry about the distributor and operator for now

  • Receive coin: The payload will be abi encoded data that looks like this: 1, uint256, fixed, tokenId, bytes32, fixed, destinationAddress, bytes, variable (has to be converted to address), amount, uint256, fixed,

  • Receive coin with data: The payload will be abi encoded data that looks like this: 2, uint256, fixed, tokenId, bytes32, fixed, destinationAddress, bytes, variable (has to be converted to address), amount, uint256, fixed, sourceChain, string, variable, sourceAddress, bytes, variable This needs to return the coin object only if called with the right capability (another channel) that proves the caller is the destinationAddress

ITS also needs to be able to send 2 calls, the call to receive coin and the call to receive coin with data, only id the right coin object is received. Since coins are only u64 some conversion might need to happen when receiving coins (decimals of 18 are too large for Sui to handle).

ITS Design

Coin Management

This module and the object it creates (CoinManagement<T>) will tell if a coin is registered as a mint/burn or lock unlock token.

To create a CoinManagement object one has to call

  • mint_burn<T>, passing in a TreasuryCap<T>.
  • lock_unlock<T>.
  • lock_unlock_funded<T> passing in some initial Coin<T> to lock.

A distributor can also be added before registerring a coin (this is not completely flushed out)

Coin Info

This module and the object it creates CoinInfo<T> will tell the ITS the information (name, symbol, decimals) for this coin. This information cannot (necesairily) be validated on chain because of how coin is implemented, which means that we have to accept whatever the registrar tells us for it. If the CoinMetadata<T> exists, we can also take it and create a 'validated' version of CoinInfo<T>.

Token Id

This module is responsible for creating tokenIds for both registerred and 'unregistered' (coins that are given to the ITS expecting a remote incoming DEPLOY_INTERCHAIN_TOKEN message) coins. We might just go back to using addresses because the UX would slightly improve, but doing it this way improves code readablility and is more in line with what Sui tries to do.

Storage

This module is responsible for managing all of the storage needs of the ITS

Service

This is the module that anyone would directly interract with. It needs to be able to do the following

  • register_coin<T>: This function takes the ITS object and mutates it by adding a coin with the specified CoinManagement<T> and CoinInfo<T>.